The invention relates to a device and a method for creating retinal fundus maps by combining two or more retinal fundus images.
In a previously known device for combining two or more retinal fundus images to create a retinal fundus map (retinal image montage), intersections between blood vessels which are shown in each fundus image are extracted as characteristic points, and correlation matching is executed on image data which are at a periphery of the intersections of blood vessels in two sheets of fundus images to find a pair having a common intersection, and two fundus images are superimposed on each other with the found intersection pair as a standard so as to create a retinal fundus map. Such technique is disclosed in Japanese patent application publication No. 2000-23921.
If photographic conditions (which may be changed according to a value of gamma, existence of optic disk, state of flare, or quantity of blood vessels) are not constant at the time of matching for blood vessel intersections, correct correspondence between the intersections is not ensured, and this matching lacks credibility. Since the matching of intersections is executed on image data, pixel data are matched with each other. Then, computational load is rather high, and it takes longer time for processing thereby. And, two or more fundus images to be compounded respectively need to have intersections of blood vessel to be matched. Therefore, it is necessary to obtain fundus images in advance so as to include such a common intersection of blood vessel when obtaining fundus images. That is, a skill for obtaining such fundus images is necessary for testers.
The invention has been made under the above-mentioned circumstances, and the object of the invention is to provide a device and method for creating retinal fundus maps wherein a stable matching is possible even if photographic conditions (which may be changed according to a value of gamma, existence of optic disk, state of flare, or quantity of blood vessels) are not constant, the computational load at the time of the matching can be reduced, and no skill is necessary for testers when obtaining fundus images.